Delayed activation of MyoD and myogenin in MKR mice. Hindlimb muscles were removed from WT and MKR mice at the ages of 0–3 weeks, 5 weeks, and 8 weeks, and subjected to Northern or Western blot analysis, as indicated below. ( a ) Northern blot analysis of MyoD levels in MKR and WT mice (upper panel). 18S RNA levels were similar in all groups (lower panel). ( b ) Western blot analysis of MyoD (upper panel) and β-actin (lower panel) immunoreactivity levels in MKR and WT mice. ( c ) Northern blot analysis of myogenin levels in MKR and WT mice (upper panel). 18S RNA levels were similar in all groups (lower panel). ( d ) Western blot analysis of myogenin (upper panel) and β-actin (lower panel) immunoreactivity levels in MKR and WT mice. Data are expressed as the mean ± SEM of three independent experiments, using five animals in each group.